gtk2/gtk/gtkglarea.c

/* GTK - The GIMP Toolkit
 *
 * gtkglarea.c: A GL drawing area
 *
 * Copyright © 2014  Emmanuele Bassi
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"

#include "config.h"
#include "gtkglarea.h"
#include "gtkintl.h"
#include "gtkstylecontext.h"
#include "gtkmarshalers.h"
#include "gtkprivate.h"
#include "gtkrender.h"
#include "gtksnapshot.h"
#include "gtknative.h"

#include <epoxy/gl.h>

/**
 * SECTION:gtkglarea
 * @Title: GtkGLArea
 * @Short_description: A widget for custom drawing with OpenGL
 *
 * #GtkGLArea is a widget that allows drawing with OpenGL.
 *
 * #GtkGLArea sets up its own #GdkGLContext for the window it creates, and
 * creates a custom GL framebuffer that the widget will do GL rendering onto.
 * It also ensures that this framebuffer is the default GL rendering target
 * when rendering.
 *
 * In order to draw, you have to connect to the #GtkGLArea::render signal,
 * or subclass #GtkGLArea and override the @GtkGLAreaClass.render() virtual
 * function.
 *
 * The #GtkGLArea widget ensures that the #GdkGLContext is associated with
 * the widget's drawing area, and it is kept updated when the size and
 * position of the drawing area changes.
 *
 * ## Drawing with GtkGLArea ##
 *
 * The simplest way to draw using OpenGL commands in a #GtkGLArea is to
 * create a widget instance and connect to the #GtkGLArea::render signal:
 *
 * |[<!-- language="C" -->

 * ]|
 *
 * The `render()` function will be called when the #GtkGLArea is ready
 * for you to draw its content:
 *
 * |[<!-- language="C" -->
 *   static gboolean
 *   render (GtkGLArea *area, GdkGLContext *context)
 *   {
 *     // inside this function it's safe to use GL; the given
 *     // #GdkGLContext has been made current to the drawable
 *     // surface used by the #GtkGLArea and the viewport has
 *     // already been set to be the size of the allocation
 *
 *     // we can start by clearing the buffer
 *     glClearColor (0, 0, 0, 0);
 *     glClear (GL_COLOR_BUFFER_BIT);
 *
 *     // draw your object
 *     // draw_an_object ();
 *
 *     // we completed our drawing; the draw commands will be
 *     // flushed at the end of the signal emission chain, and
 *     // the buffers will be drawn on the window
 *     return TRUE;
 *   }
 *
 *   void setup_glarea (void)
 *   {
 *     // create a GtkGLArea instance
 *     GtkWidget *gl_area = gtk_gl_area_new ();
 *
 *     // connect to the "render" signal
 *     g_signal_connect (gl_area, "render", G_CALLBACK (render), NULL);
 *   }
 * ]|
 *
 * If you need to initialize OpenGL state, e.g. buffer objects or
 * shaders, you should use the #GtkWidget::realize signal; you
 * can use the #GtkWidget::unrealize signal to clean up. Since the
 * #GdkGLContext creation and initialization may fail, you will
 * need to check for errors, using gtk_gl_area_get_error(). An example
 * of how to safely initialize the GL state is:
 *
 * |[<!-- language="C" -->
 *   static void
 *   on_realize (GtkGLarea *area)
 *   {
 *     // We need to make the context current if we want to
 *     // call GL API
 *     gtk_gl_area_make_current (area);
 *
 *     // If there were errors during the initialization or
 *     // when trying to make the context current, this
 *     // function will return a #GError for you to catch
 *     if (gtk_gl_area_get_error (area) != NULL)
 *       return;
 *
 *     // You can also use gtk_gl_area_set_error() in order
 *     // to show eventual initialization errors on the
 *     // GtkGLArea widget itself
 *     GError *internal_error = NULL;
 *     init_buffer_objects (&error);
 *     if (error != NULL)
 *       {
 *         gtk_gl_area_set_error (area, error);
 *         g_error_free (error);
 *         return;
 *       }
 *
 *     init_shaders (&error);
 *     if (error != NULL)
 *       {
 *         gtk_gl_area_set_error (area, error);
 *         g_error_free (error);
 *         return;
 *       }
 *   }
 * ]|
 *
 * If you need to change the options for creating the #GdkGLContext
 * you should use the #GtkGLArea::create-context signal.
 */

typedef struct {
  guint id;
  int width;
  int height;
  GdkTexture *holder;
} Texture;

typedef struct {
  GdkGLContext *context;
  GError *error;

  gboolean have_buffers;

  int required_gl_version;

  guint frame_buffer;
  guint depth_stencil_buffer;
  Texture *texture;
  GList *textures;

  gboolean has_depth_buffer;
  gboolean has_stencil_buffer;

  gboolean needs_resize;
  gboolean needs_render;
  gboolean auto_render;
  gboolean use_es;
} GtkGLAreaPrivate;

enum {
  PROP_0,

  PROP_CONTEXT,
  PROP_HAS_DEPTH_BUFFER,
  PROP_HAS_STENCIL_BUFFER,
  PROP_USE_ES,

  PROP_AUTO_RENDER,

  LAST_PROP
};

static GParamSpec *obj_props[LAST_PROP] = { NULL, };

enum {
  RENDER,
  RESIZE,
  CREATE_CONTEXT,

  LAST_SIGNAL
};

static void gtk_gl_area_allocate_buffers (GtkGLArea *area);
static void gtk_gl_area_allocate_texture (GtkGLArea *area);

static guint area_signals[LAST_SIGNAL] = { 0, };

G_DEFINE_TYPE_WITH_PRIVATE (GtkGLArea, gtk_gl_area, GTK_TYPE_WIDGET)

static void
gtk_gl_area_set_property (GObject      *gobject,
                          guint         prop_id,
                          const GValue *value,
                          GParamSpec   *pspec)
{
  GtkGLArea *self = GTK_GL_AREA (gobject);

  switch (prop_id)
    {
    case PROP_AUTO_RENDER:
      gtk_gl_area_set_auto_render (self, g_value_get_boolean (value));
      break;

    case PROP_HAS_DEPTH_BUFFER:
      gtk_gl_area_set_has_depth_buffer (self, g_value_get_boolean (value));
      break;

    case PROP_HAS_STENCIL_BUFFER:
      gtk_gl_area_set_has_stencil_buffer (self, g_value_get_boolean (value));
      break;

    case PROP_USE_ES:
      gtk_gl_area_set_use_es (self, g_value_get_boolean (value));
      break;

    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
    }
}

static void
gtk_gl_area_get_property (GObject    *gobject,
                          guint       prop_id,
                          GValue     *value,
                          GParamSpec *pspec)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (GTK_GL_AREA (gobject));

  switch (prop_id)
    {
    case PROP_AUTO_RENDER:
      g_value_set_boolean (value, priv->auto_render);
      break;

    case PROP_HAS_DEPTH_BUFFER:
      g_value_set_boolean (value, priv->has_depth_buffer);
      break;

    case PROP_HAS_STENCIL_BUFFER:
      g_value_set_boolean (value, priv->has_stencil_buffer);
      break;

    case PROP_CONTEXT:
      g_value_set_object (value, priv->context);
      break;

    case PROP_USE_ES:
      g_value_set_boolean (value, priv->use_es);
      break;

    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
    }
}

static void
gtk_gl_area_realize (GtkWidget *widget)
{
  GtkGLArea *area = GTK_GL_AREA (widget);
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  GTK_WIDGET_CLASS (gtk_gl_area_parent_class)->realize (widget);

  g_clear_error (&priv->error);
  priv->context = NULL;
  g_signal_emit (area, area_signals[CREATE_CONTEXT], 0, &priv->context);

  /* In case the signal failed, but did not set an error */
  if (priv->context == NULL && priv->error == NULL)
    g_set_error_literal (&priv->error, GDK_GL_ERROR,
                         GDK_GL_ERROR_NOT_AVAILABLE,
                         _("OpenGL context creation failed"));

  priv->needs_resize = TRUE;
}

static void
gtk_gl_area_notify (GObject    *object,
                    GParamSpec *pspec)
{
  if (strcmp (pspec->name, "scale-factor") == 0)
    {
      GtkGLArea *area = GTK_GL_AREA (object);
      GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

      priv->needs_resize = TRUE;
    }

  if (G_OBJECT_CLASS (gtk_gl_area_parent_class)->notify)
    G_OBJECT_CLASS (gtk_gl_area_parent_class)->notify (object, pspec);
}

static GdkGLContext *
gtk_gl_area_real_create_context (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  GtkWidget *widget = GTK_WIDGET (area);
  GError *error = NULL;
  GdkGLContext *context;

  context = gdk_surface_create_gl_context (gtk_native_get_surface (gtk_widget_get_native (widget)), &error);
  if (error != NULL)
    {
      gtk_gl_area_set_error (area, error);
      g_clear_object (&context);
      g_clear_error (&error);
      return NULL;
    }

  gdk_gl_context_set_use_es (context, priv->use_es);
  gdk_gl_context_set_required_version (context,
                                       priv->required_gl_version / 10,
                                       priv->required_gl_version % 10);

  gdk_gl_context_realize (context, &error);
  if (error != NULL)
    {
      gtk_gl_area_set_error (area, error);
      g_clear_object (&context);
      g_clear_error (&error);
      return NULL;
    }

  return context;
}

static void
gtk_gl_area_resize (GtkGLArea *area, int width, int height)
{
  glViewport (0, 0, width, height);
}

/*
 * Creates all the buffer objects needed for rendering the scene
 */
static void
gtk_gl_area_ensure_buffers (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  GtkWidget *widget = GTK_WIDGET (area);

  gtk_widget_realize (widget);

  if (priv->context == NULL)
    return;

  if (priv->have_buffers)
    return;

  priv->have_buffers = TRUE;

  glGenFramebuffersEXT (1, &priv->frame_buffer);

  if ((priv->has_depth_buffer || priv->has_stencil_buffer))
    {
      if (priv->depth_stencil_buffer == 0)
        glGenRenderbuffersEXT (1, &priv->depth_stencil_buffer);
    }
  else if (priv->depth_stencil_buffer != 0)
    {
      /* Delete old depth/stencil buffer */
      glDeleteRenderbuffersEXT (1, &priv->depth_stencil_buffer);
      priv->depth_stencil_buffer = 0;
    }

  gtk_gl_area_allocate_buffers (area);
}

static void
delete_one_texture (gpointer data)
{
  Texture *texture = data;

  if (texture->holder)
    gdk_gl_texture_release (GDK_GL_TEXTURE (texture->holder));

  if (texture->id != 0)
    {
      glDeleteTextures (1, &texture->id);
      texture->id = 0;
    }

  g_free (texture);
}

static void
gtk_gl_area_ensure_texture (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  GtkWidget *widget = GTK_WIDGET (area);

  gtk_widget_realize (widget);

  if (priv->context == NULL)
    return;

  if (priv->texture == NULL)
    {
      GList *l, *link;

      l = priv->textures;
      while (l)
        {
          Texture *texture = l->data;
          link = l;
          l = l->next;

          if (texture->holder)
            continue;

          priv->textures = g_list_delete_link (priv->textures, link);

          if (priv->texture == NULL)
            priv->texture = texture;
          else
            delete_one_texture (texture);
        }
    }

  if (priv->texture == NULL)
    {
      priv->texture = g_new (Texture, 1);

      priv->texture->width = 0;
      priv->texture->height = 0;
      priv->texture->holder = NULL;

      glGenTextures (1, &priv->texture->id);
    }

  gtk_gl_area_allocate_texture (area);
}

/*
 * Allocates space of the right type and size for all the buffers
 */
static void
gtk_gl_area_allocate_buffers (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  GtkWidget *widget = GTK_WIDGET (area);
  int scale, width, height;

  if (priv->context == NULL)
    return;

  scale = gtk_widget_get_scale_factor (widget);
  width = gtk_widget_get_width (widget) * scale;
  height = gtk_widget_get_height (widget) * scale;

  if (priv->has_depth_buffer || priv->has_stencil_buffer)
    {
      glBindRenderbuffer (GL_RENDERBUFFER, priv->depth_stencil_buffer);
      if (priv->has_stencil_buffer)
        glRenderbufferStorage (GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, width, height);
      else
        glRenderbufferStorage (GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, width, height);
    }

  priv->needs_render = TRUE;
}

static void
gtk_gl_area_allocate_texture (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  GtkWidget *widget = GTK_WIDGET (area);
  int scale, width, height;

  if (priv->context == NULL)
    return;

  if (priv->texture == NULL)
    return;

  g_assert (priv->texture->holder == NULL);

  scale = gtk_widget_get_scale_factor (widget);
  width = gtk_widget_get_width (widget) * scale;
  height = gtk_widget_get_height (widget) * scale;

  if (priv->texture->width != width ||
      priv->texture->height != height)
    {
      glBindTexture (GL_TEXTURE_2D, priv->texture->id);
      glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
      glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
      glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
      glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

      if (gdk_gl_context_get_use_es (priv->context))
        glTexImage2D (GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
      else
        glTexImage2D (GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);

      priv->texture->width = width;
      priv->texture->height = height;
    }
}

/**
 * gtk_gl_area_attach_buffers:
 * @area: a #GtkGLArea
 *
 * Ensures that the @area framebuffer object is made the current draw
 * and read target, and that all the required buffers for the @area
 * are created and bound to the frambuffer.
 *
 * This function is automatically called before emitting the
 * #GtkGLArea::render signal, and doesn't normally need to be called
 * by application code.
 */
void
gtk_gl_area_attach_buffers (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  if (priv->context == NULL)
    return;

  gtk_gl_area_make_current (area);

  if (priv->texture == NULL)
    gtk_gl_area_ensure_texture (area);
  else if (priv->needs_resize)
    gtk_gl_area_allocate_texture (area);

  if (!priv->have_buffers)
    gtk_gl_area_ensure_buffers (area);
  else if (priv->needs_resize)
    gtk_gl_area_allocate_buffers (area);

  glBindFramebufferEXT (GL_FRAMEBUFFER_EXT, priv->frame_buffer);

  if (priv->texture != NULL)
    glFramebufferTexture2D (GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
                            GL_TEXTURE_2D, priv->texture->id, 0);

  if (priv->depth_stencil_buffer)
    {
      if (priv->has_depth_buffer)
        glFramebufferRenderbufferEXT (GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT,
                                      GL_RENDERBUFFER_EXT, priv->depth_stencil_buffer);
      if (priv->has_stencil_buffer)
        glFramebufferRenderbufferEXT (GL_FRAMEBUFFER_EXT, GL_STENCIL_ATTACHMENT_EXT,
                                      GL_RENDERBUFFER_EXT, priv->depth_stencil_buffer);
    }
}

static void
gtk_gl_area_delete_buffers (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  if (priv->context == NULL)
    return;

  priv->have_buffers = FALSE;

  if (priv->depth_stencil_buffer != 0)
    {
      glDeleteRenderbuffersEXT (1, &priv->depth_stencil_buffer);
      priv->depth_stencil_buffer = 0;
    }

  if (priv->frame_buffer != 0)
    {
      glBindFramebufferEXT (GL_FRAMEBUFFER_EXT, 0);
      glDeleteFramebuffersEXT (1, &priv->frame_buffer);
      priv->frame_buffer = 0;
    }
}

static void
gtk_gl_area_delete_textures (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  if (priv->texture)
    {
      delete_one_texture (priv->texture);
      priv->texture = NULL;
    }

  /* FIXME: we need to explicitly release all outstanding
   * textures here, otherwise release_texture will get called
   * later and access freed memory.
   */
  g_list_free_full (priv->textures, delete_one_texture);
  priv->textures = NULL;
}

static void
gtk_gl_area_unrealize (GtkWidget *widget)
{
  GtkGLArea *area = GTK_GL_AREA (widget);
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  if (priv->context != NULL)
    {
      gtk_gl_area_make_current (area);
      gtk_gl_area_delete_buffers (area);
      gtk_gl_area_delete_textures (area);

      /* Make sure to unset the context if current */
      if (priv->context == gdk_gl_context_get_current ())
        gdk_gl_context_clear_current ();
    }

  g_clear_object (&priv->context);
  g_clear_error (&priv->error);

  GTK_WIDGET_CLASS (gtk_gl_area_parent_class)->unrealize (widget);
}

static void
gtk_gl_area_size_allocate (GtkWidget *widget,
                           int        width,
                           int        height,
                           int        baseline)
{
  GtkGLArea *area = GTK_GL_AREA (widget);
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  GTK_WIDGET_CLASS (gtk_gl_area_parent_class)->size_allocate (widget, width, height, baseline);

  if (gtk_widget_get_realized (widget))
    priv->needs_resize = TRUE;
}

static void
gtk_gl_area_draw_error_screen (GtkGLArea   *area,
                               GtkSnapshot *snapshot,
                               gint         width,
                               gint         height)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  PangoLayout *layout;
  int layout_height;

  layout = gtk_widget_create_pango_layout (GTK_WIDGET (area),
                                           priv->error->message);
  pango_layout_set_width (layout, width * PANGO_SCALE);
  pango_layout_set_alignment (layout, PANGO_ALIGN_CENTER);
  pango_layout_get_pixel_size (layout, NULL, &layout_height);

  gtk_snapshot_render_layout (snapshot,
                              gtk_widget_get_style_context (GTK_WIDGET (area)),
                              0, (height - layout_height) / 2,
                              layout);

  g_object_unref (layout);
}

static void
release_texture (gpointer data)
{
  Texture *texture = data;
  texture->holder = NULL;
}

static void
gtk_gl_area_snapshot (GtkWidget   *widget,
                      GtkSnapshot *snapshot)
{
  GtkGLArea *area = GTK_GL_AREA (widget);
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
  gboolean unused;
  int w, h, scale;
  GLenum status;

  scale = gtk_widget_get_scale_factor (widget);
  w = gtk_widget_get_width (widget) * scale;
  h = gtk_widget_get_height (widget) * scale;

  if (w == 0 || h == 0)
    return;

  if (priv->error != NULL)
    {
      gtk_gl_area_draw_error_screen (area,
                                     snapshot,
                                     gtk_widget_get_width (widget),
                                     gtk_widget_get_height (widget));
      return;
    }

  if (priv->context == NULL)
    return;

  gtk_gl_area_make_current (area);

  gtk_gl_area_attach_buffers (area);

 if (priv->has_depth_buffer)
   glEnable (GL_DEPTH_TEST);
 else
   glDisable (GL_DEPTH_TEST);

  status = glCheckFramebufferStatusEXT (GL_FRAMEBUFFER_EXT);
  if (status == GL_FRAMEBUFFER_COMPLETE_EXT)
    {
      Texture *texture;

      if (priv->needs_render || priv->auto_render)
        {
          if (priv->needs_resize)
            {
              g_signal_emit (area, area_signals[RESIZE], 0, w, h, NULL);
              priv->needs_resize = FALSE;
            }

          g_signal_emit (area, area_signals[RENDER], 0, priv->context, &unused);
        }

      priv->needs_render = FALSE;

      texture = priv->texture;
      priv->texture = NULL;
      priv->textures = g_list_prepend (priv->textures, texture);

      texture->holder = gdk_gl_texture_new (priv->context,
                                            texture->id,
                                            texture->width,
                                            texture->height,
                                            release_texture, texture);

      gtk_snapshot_append_texture (snapshot,
                                   texture->holder,
                                   &GRAPHENE_RECT_INIT (0, 0,
                                                        gtk_widget_get_width (widget),
                                                        gtk_widget_get_height (widget)));

      g_object_unref (texture->holder);
    }
  else
    {
      g_warning ("fb setup not supported (%x)", status);
    }
}

static gboolean
create_context_accumulator (GSignalInvocationHint *ihint,
                            GValue *return_accu,
                            const GValue *handler_return,
                            gpointer data)
{
  g_value_copy (handler_return, return_accu);

  /* stop after the first handler returning a valid object */
  return g_value_get_object (handler_return) == NULL;
}

static void
gtk_gl_area_class_init (GtkGLAreaClass *klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);

  klass->resize = gtk_gl_area_resize;
  klass->create_context = gtk_gl_area_real_create_context;

  widget_class->realize = gtk_gl_area_realize;
  widget_class->unrealize = gtk_gl_area_unrealize;
  widget_class->size_allocate = gtk_gl_area_size_allocate;
  widget_class->snapshot = gtk_gl_area_snapshot;

  gtk_widget_class_set_accessible_role (widget_class, ATK_ROLE_DRAWING_AREA);

  /**
   * GtkGLArea:context:
   *
   * The #GdkGLContext used by the #GtkGLArea widget.
   *
   * The #GtkGLArea widget is responsible for creating the #GdkGLContext
   * instance. If you need to render with other kinds of buffers (stencil,
   * depth, etc), use render buffers.
   */
  obj_props[PROP_CONTEXT] =
    g_param_spec_object ("context",
                         P_("Context"),
                         P_("The GL context"),
                         GDK_TYPE_GL_CONTEXT,
                         G_PARAM_READABLE |
                         G_PARAM_STATIC_STRINGS);

  /**
   * GtkGLArea:auto-render:
   *
   * If set to %TRUE the #GtkGLArea::render signal will be emitted every time
   * the widget draws. This is the default and is useful if drawing the widget
   * is faster.
   *
   * If set to %FALSE the data from previous rendering is kept around and will
   * be used for drawing the widget the next time, unless the window is resized.
   * In order to force a rendering gtk_gl_area_queue_render() must be called.
   * This mode is useful when the scene changes seldomly, but takes a long time
   * to redraw.
   */
  obj_props[PROP_AUTO_RENDER] =
    g_param_spec_boolean ("auto-render",
                          P_("Auto render"),
                          P_("Whether the GtkGLArea renders on each redraw"),
                          TRUE,
                          GTK_PARAM_READWRITE |
                          G_PARAM_STATIC_STRINGS |
                          G_PARAM_EXPLICIT_NOTIFY);

  /**
   * GtkGLArea:has-depth-buffer:
   *
   * If set to %TRUE the widget will allocate and enable a depth buffer for the
   * target framebuffer.
   */
  obj_props[PROP_HAS_DEPTH_BUFFER] =
    g_param_spec_boolean ("has-depth-buffer",
                          P_("Has depth buffer"),
                          P_("Whether a depth buffer is allocated"),
                          FALSE,
                          GTK_PARAM_READWRITE |
                          G_PARAM_STATIC_STRINGS |
                          G_PARAM_EXPLICIT_NOTIFY);

  /**
   * GtkGLArea:has-stencil-buffer:
   *
   * If set to %TRUE the widget will allocate and enable a stencil buffer for the
   * target framebuffer.
   */
  obj_props[PROP_HAS_STENCIL_BUFFER] =
    g_param_spec_boolean ("has-stencil-buffer",
                          P_("Has stencil buffer"),
                          P_("Whether a stencil buffer is allocated"),
                          FALSE,
                          GTK_PARAM_READWRITE |
                          G_PARAM_STATIC_STRINGS |
                          G_PARAM_EXPLICIT_NOTIFY);

  /**
   * GtkGLArea:use-es:
   *
   * If set to %TRUE the widget will try to create a #GdkGLContext using
   * OpenGL ES instead of OpenGL.
   *
   * See also: gdk_gl_context_set_use_es()
   */
  obj_props[PROP_USE_ES] =
    g_param_spec_boolean ("use-es",
                          P_("Use OpenGL ES"),
                          P_("Whether the context uses OpenGL or OpenGL ES"),
                          FALSE,
                          GTK_PARAM_READWRITE |
                          G_PARAM_STATIC_STRINGS |
                          G_PARAM_EXPLICIT_NOTIFY);

  gobject_class->set_property = gtk_gl_area_set_property;
  gobject_class->get_property = gtk_gl_area_get_property;
  gobject_class->notify = gtk_gl_area_notify;

  g_object_class_install_properties (gobject_class, LAST_PROP, obj_props);

  /**
   * GtkGLArea::render:
   * @area: the #GtkGLArea that emitted the signal
   * @context: the #GdkGLContext used by @area
   *
   * The ::render signal is emitted every time the contents
   * of the #GtkGLArea should be redrawn.
   *
   * The @context is bound to the @area prior to emitting this function,
   * and the buffers are painted to the window once the emission terminates.
   *
   * Returns: %TRUE to stop other handlers from being invoked for the event.
   *   %FALSE to propagate the event further.
   */
  area_signals[RENDER] =
    g_signal_new (I_("render"),
                  G_TYPE_FROM_CLASS (gobject_class),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GtkGLAreaClass, render),
                  _gtk_boolean_handled_accumulator, NULL,
                  NULL,
                  G_TYPE_BOOLEAN, 1,
                  GDK_TYPE_GL_CONTEXT);

  /**
   * GtkGLArea::resize:
   * @area: the #GtkGLArea that emitted the signal
   * @width: the width of the viewport
   * @height: the height of the viewport
   *
   * The ::resize signal is emitted once when the widget is realized, and
   * then each time the widget is changed while realized. This is useful
   * in order to keep GL state up to date with the widget size, like for
   * instance camera properties which may depend on the width/height ratio.
   *
   * The GL context for the area is guaranteed to be current when this signal
   * is emitted.
   *
   * The default handler sets up the GL viewport.
   */
  area_signals[RESIZE] =
    g_signal_new (I_("resize"),
                  G_TYPE_FROM_CLASS (klass),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GtkGLAreaClass, resize),
                  NULL, NULL,
                  _gtk_marshal_VOID__INT_INT,
                  G_TYPE_NONE, 2, G_TYPE_INT, G_TYPE_INT);

  /**
   * GtkGLArea::create-context:
   * @area: the #GtkGLArea that emitted the signal
   * @error: (allow-none): location to store error information on failure
   *
   * The ::create-context signal is emitted when the widget is being
   * realized, and allows you to override how the GL context is
   * created. This is useful when you want to reuse an existing GL
   * context, or if you want to try creating different kinds of GL
   * options.
   *
   * If context creation fails then the signal handler can use
   * gtk_gl_area_set_error() to register a more detailed error
   * of how the construction failed.
   *
   * Returns: (transfer full): a newly created #GdkGLContext;
   *     the #GtkGLArea widget will take ownership of the returned value.
   */
  area_signals[CREATE_CONTEXT] =
    g_signal_new (I_("create-context"),
                  G_TYPE_FROM_CLASS (klass),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GtkGLAreaClass, create_context),
                  create_context_accumulator, NULL,
                  _gtk_marshal_OBJECT__VOID,
                  GDK_TYPE_GL_CONTEXT, 0);
}

static void
gtk_gl_area_init (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  priv->auto_render = TRUE;
  priv->needs_render = TRUE;
  priv->required_gl_version = 0;
}

/**
 * gtk_gl_area_new:
 *
 * Creates a new #GtkGLArea widget.
 *
 * Returns: a new #GtkGLArea
 */
GtkWidget *
gtk_gl_area_new (void)
{
  return g_object_new (GTK_TYPE_GL_AREA, NULL);
}

/**
 * gtk_gl_area_set_error:
 * @area: a #GtkGLArea
 * @error: (allow-none): a new #GError, or %NULL to unset the error
 *
 * Sets an error on the area which will be shown instead of the
 * GL rendering. This is useful in the #GtkGLArea::create-context
 * signal if GL context creation fails.
 */
void
gtk_gl_area_set_error (GtkGLArea    *area,
                       const GError *error)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  g_clear_error (&priv->error);
  if (error)
    priv->error = g_error_copy (error);
}

/**
 * gtk_gl_area_get_error:
 * @area: a #GtkGLArea
 *
 * Gets the current error set on the @area.
 *
 * Returns: (nullable) (transfer none): the #GError or %NULL
 */
GError *
gtk_gl_area_get_error (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), NULL);

  return priv->error;
}

/**
 * gtk_gl_area_set_use_es:
 * @area: a #GtkGLArea
 * @use_es: whether to use OpenGL or OpenGL ES
 *
 * Sets whether the @area should create an OpenGL or an OpenGL ES context.
 *
 * You should check the capabilities of the #GdkGLContext before drawing
 * with either API.
 */
void
gtk_gl_area_set_use_es (GtkGLArea *area,
                        gboolean   use_es)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));
  g_return_if_fail (!gtk_widget_get_realized (GTK_WIDGET (area)));

  use_es = !!use_es;

  if (priv->use_es != use_es)
    {
      priv->use_es = use_es;

      g_object_notify_by_pspec (G_OBJECT (area), obj_props[PROP_USE_ES]);
    }
}

/**
 * gtk_gl_area_get_use_es:
 * @area: a #GtkGLArea
 *
 * Retrieves the value set by gtk_gl_area_set_use_es().
 *
 * Returns: %TRUE if the #GtkGLArea should create an OpenGL ES context
 *   and %FALSE otherwise
 */
gboolean
gtk_gl_area_get_use_es (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), FALSE);

  return priv->use_es;
}

/**
 * gtk_gl_area_set_required_version:
 * @area: a #GtkGLArea
 * @major: the major version
 * @minor: the minor version
 *
 * Sets the required version of OpenGL to be used when creating the context
 * for the widget.
 *
 * This function must be called before the area has been realized.
 */
void
gtk_gl_area_set_required_version (GtkGLArea *area,
                                  gint       major,
                                  gint       minor)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));
  g_return_if_fail (!gtk_widget_get_realized (GTK_WIDGET (area)));

  priv->required_gl_version = major * 10 + minor;
}

/**
 * gtk_gl_area_get_required_version:
 * @area: a #GtkGLArea
 * @major: (out): return location for the required major version
 * @minor: (out): return location for the required minor version
 *
 * Retrieves the required version of OpenGL set
 * using gtk_gl_area_set_required_version().
 */
void
gtk_gl_area_get_required_version (GtkGLArea *area,
                                  gint      *major,
                                  gint      *minor)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  if (major != NULL)
    *major = priv->required_gl_version / 10;
  if (minor != NULL)
    *minor = priv->required_gl_version % 10;
}

/**
 * gtk_gl_area_get_has_depth_buffer:
 * @area: a #GtkGLArea
 *
 * Returns whether the area has a depth buffer.
 *
 * Returns: %TRUE if the @area has a depth buffer, %FALSE otherwise
 */
gboolean
gtk_gl_area_get_has_depth_buffer (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), FALSE);

  return priv->has_depth_buffer;
}

/**
 * gtk_gl_area_set_has_depth_buffer:
 * @area: a #GtkGLArea
 * @has_depth_buffer: %TRUE to add a depth buffer
 *
 * If @has_depth_buffer is %TRUE the widget will allocate and
 * enable a depth buffer for the target framebuffer. Otherwise
 * there will be none.
 */
void
gtk_gl_area_set_has_depth_buffer (GtkGLArea *area,
                                  gboolean   has_depth_buffer)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  has_depth_buffer = !!has_depth_buffer;

  if (priv->has_depth_buffer != has_depth_buffer)
    {
      priv->has_depth_buffer = has_depth_buffer;

      g_object_notify (G_OBJECT (area), "has-depth-buffer");

      priv->have_buffers = FALSE;
    }
}

/**
 * gtk_gl_area_get_has_stencil_buffer:
 * @area: a #GtkGLArea
 *
 * Returns whether the area has a stencil buffer.
 *
 * Returns: %TRUE if the @area has a stencil buffer, %FALSE otherwise
 */
gboolean
gtk_gl_area_get_has_stencil_buffer (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), FALSE);

  return priv->has_stencil_buffer;
}

/**
 * gtk_gl_area_set_has_stencil_buffer:
 * @area: a #GtkGLArea
 * @has_stencil_buffer: %TRUE to add a stencil buffer
 *
 * If @has_stencil_buffer is %TRUE the widget will allocate and
 * enable a stencil buffer for the target framebuffer. Otherwise
 * there will be none.
 */
void
gtk_gl_area_set_has_stencil_buffer (GtkGLArea *area,
                                    gboolean   has_stencil_buffer)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  has_stencil_buffer = !!has_stencil_buffer;

  if (priv->has_stencil_buffer != has_stencil_buffer)
    {
      priv->has_stencil_buffer = has_stencil_buffer;

      g_object_notify (G_OBJECT (area), "has-stencil-buffer");

      priv->have_buffers = FALSE;
    }
}

/**
 * gtk_gl_area_queue_render:
 * @area: a #GtkGLArea
 *
 * Marks the currently rendered data (if any) as invalid, and queues
 * a redraw of the widget, ensuring that the #GtkGLArea::render signal
 * is emitted during the draw.
 *
 * This is only needed when the gtk_gl_area_set_auto_render() has
 * been called with a %FALSE value. The default behaviour is to
 * emit #GtkGLArea::render on each draw.
 */
void
gtk_gl_area_queue_render (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  priv->needs_render = TRUE;

  gtk_widget_queue_draw (GTK_WIDGET (area));
}


/**
 * gtk_gl_area_get_auto_render:
 * @area: a #GtkGLArea
 *
 * Returns whether the area is in auto render mode or not.
 *
 * Returns: %TRUE if the @area is auto rendering, %FALSE otherwise
 */
gboolean
gtk_gl_area_get_auto_render (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), FALSE);

  return priv->auto_render;
}

/**
 * gtk_gl_area_set_auto_render:
 * @area: a #GtkGLArea
 * @auto_render: a boolean
 *
 * If @auto_render is %TRUE the #GtkGLArea::render signal will be
 * emitted every time the widget draws. This is the default and is
 * useful if drawing the widget is faster.
 *
 * If @auto_render is %FALSE the data from previous rendering is kept
 * around and will be used for drawing the widget the next time,
 * unless the window is resized. In order to force a rendering
 * gtk_gl_area_queue_render() must be called. This mode is useful when
 * the scene changes seldomly, but takes a long time to redraw.
 */
void
gtk_gl_area_set_auto_render (GtkGLArea *area,
                             gboolean   auto_render)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));

  auto_render = !!auto_render;

  if (priv->auto_render != auto_render)
    {
      priv->auto_render = auto_render;

      g_object_notify (G_OBJECT (area), "auto-render");

      if (auto_render)
        gtk_widget_queue_draw (GTK_WIDGET (area));
    }
}

/**
 * gtk_gl_area_get_context:
 * @area: a #GtkGLArea
 *
 * Retrieves the #GdkGLContext used by @area.
 *
 * Returns: (transfer none): the #GdkGLContext
 */
GdkGLContext *
gtk_gl_area_get_context (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_val_if_fail (GTK_IS_GL_AREA (area), NULL);

  return priv->context;
}

/**
 * gtk_gl_area_make_current:
 * @area: a #GtkGLArea
 *
 * Ensures that the #GdkGLContext used by @area is associated with
 * the #GtkGLArea.
 *
 * This function is automatically called before emitting the
 * #GtkGLArea::render signal, and doesn't normally need to be called
 * by application code.
 */
void
gtk_gl_area_make_current (GtkGLArea *area)
{
  GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);

  g_return_if_fail (GTK_IS_GL_AREA (area));
  g_return_if_fail (gtk_widget_get_realized (GTK_WIDGET (area)));

  if (priv->context != NULL)
    gdk_gl_context_make_current (priv->context);
}